A modern mobile device can incorporate functions of a computer, a cellular transceiver, and a wireless (e.g., WiFi™) transceiver. For example, the mobile device can perform traditional computer functions, such as executing application programs, storing various data, and displaying digital images. These functions can be performed in an application subsystem of the mobile device. The application subsystem can include an application processor, an application operating system, and various input/output devices. Using the cellular transceiver, the mobile device can function as a cellular phone. Using the wireless transceiver, the mobile device can access a communications network through one or more wireless access points.
Some of the functions performed by a mobile device can be functions based on a geofence. A geofence can include a virtual boundary of a real-world geographic area. The mobile device can be programmed to perform a task when the mobile device is located inside of a geofence. The mobile device can determine whether the mobile device is located inside of a geofence by comparing a location of the mobile device with coordinates of the geographic area. A conventional mobile device can determine the current location using cell tower triangulation or global positioning system (GPS) functions. The application processor of the mobile device can perform the triangulation or GPS calculations.